Semiconductor device and manufacturing method of the same

ABSTRACT

An object is to provide a semiconductor device with high aperture ratio or a manufacturing method thereof. Another object is to provide semiconductor device with low power consumption or a manufacturing method thereof. A light-transmitting conductive layer which functions as a gate electrode, a gate insulating film formed over the light-transmitting conductive layer, a semiconductor layer formed over the light-transmitting conductive layer which functions as the gate electrode with the gate insulating film interposed therebetween, and a light-transmitting conductive layer which is electrically connected to the semiconductor layer and functions as source and drain electrodes are included.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to a semiconductor device, a display device, aproducing method thereof, or a method using the semiconductor device orthe display device. In specific, this invention relates to asemiconductor device and a display device each including alight-transmitting semiconductor layer, a producing method thereof, or amethod using the semiconductor device or the display device. Further inspecific, this invention relates to a liquid crystal display deviceincluding a light-transmitting semiconductor layer, a manufacturingmethod thereof, or a method the liquid crystal display device.

2. Description of the Related Art

In recent years, flat panel displays such as liquid crystal displays(LCDs) are becoming widespread. In specific, active-matrix LCDs providedwith a transistor in each pixel are often used. As the transistor, theone which employs amorphous (non-crystalline) silicon or poly(polycrystalline) silicon for a semiconductor layer is widely used.

However, instead of the transistors formed using such silicon materials,transistors including light-transmitting semiconductor layers areconsidered. Further, a technique which increases an aperture ratio byemploying light-transmitting electrodes as gate electrodes and sourceand drain electrodes is considered (see Reference 1 and Reference 2).

-   Reference 1: Japanese Published Patent Application No. 2007-123700-   Reference 2: Japanese Published Patent Application No. 2007-81362

In general, a wiring for connecting elements such as transistors to eachother is formed by extending conductive layers for forming a gateelectrode and source and drain electrodes, whereby the wiring is formedin the same island as the conductive layers. Accordingly, a wiring forconnecting gate of a transistor to gate of another transistor (such awiring is called a gate wiring) is formed using the same layer structureand material as a gate electrode of the transistor; and a wiring forconnecting source of the transistor to source of another transistor(such a wiring is called a source wiring) is formed using the same layerstructure and material as a source electrode of the transistor, in manycases. Therefore, in the case where the gate electrode and the sourceand drain electrodes are formed using a light-transmitting material, thegate wiring and the source wiring are also formed using thelight-transmitting material in many cases, like the gate electrode andthe source and drain electrodes.

However, in general, as compared to a conductive material havinglight-shielding property and a reflecting property, such as aluminum(Al), molybdenum (Mo), titanium (Ti), tungsten (W), neodymium (Nd),Copper (Cu), or silver (Ag), a light-transmitting conductive materialsuch as indium tin oxide (ITO), indium zinc oxide (IZO), or indium tinzinc oxide (ITZO) has low conductivity. Accordingly, if a wiring isformed using a light-transmitting conductive material, wiring resistancebecomes high. For example, in the case where a large display device ismanufactured, wiring resistance becomes very high because a wiring islong. As wiring resistance increases, the waveform of a signal which istransmitted through the wiring becomes distorted, resulting in a lowvoltage supply due to a voltage drop through the wiring resistance.Therefore, it is difficult to supply normal voltage and current, wherebynormal display and operation become difficult.

On the other hand, in the case where a gate wiring and a source wiringare formed using a light-shielding conductive material by using thelight-shielding conductive material for the gate electrode and thesource and drain electrodes, distortion of the waveform of the signalcan be suppressed due to an increase in the conductivity of the wiring.However, since a light-shielding material is used for the gate electrodeand the source and drain electrodes, aperture ratio decreases and powerconsumption becomes high.

In addition, in terms of display performance, high storage capacitanceand higher aperture ratio are demanded for pixels. Pixels each havinghigh aperture ratio increase the use efficiency of light, so that powersaving and miniaturization of a display device can be achieved. Inrecent years, the size of pixels has been miniaturized and images withhigher definition are demanded. The miniaturization of the size of thepixel causes a decrease in the aperture ratio of the pixel because oflarge formation area for transistors and wirings which occupies onepixel. Accordingly, in order to obtain a high aperture ratio in eachpixel in a regulation size, the circuit configuration of the pixel needsto have an efficient layout of necessary components.

In view of the foregoing problems, one object of an embodiment in thisinvention is to provide a semiconductor device with high aperture ratioand a manufacturing method thereof. In addition, one object of oneembodiment in this invention is to provide a semiconductor device withlow power consumption and a manufacturing method thereof.

In order to solve the above problem, one embodiment of this invention isa semiconductor device which includes a gate wiring including a gateelectrode, in which a first conductive film and a second conductive filmare stacked in this order, a gate insulating film covering the gateelectrode and the gate wiring, an island-shaped semiconductor filmprovided over the gate electrode with the gate insulating filminterposed therebetween, a source wiring including a source electrode,in which a third conductive film and a fourth conductive film arestacked in this order, an interlayer insulating film covering theisland-shaped semiconductor film and the source wiring including thesource electrode, a pixel electrode provided over the interlayerinsulating film and electrically connected to the island-shapedsemiconductor film, and a capacitor wiring. The gate electrode is formedof the first conductive film. The gate wiring is formed of the firstconductive film and the second conductive film. The source electrode isformed of the third conductive film. The source wiring is formed of thethird conductive film and the fourth conductive film.

Further, one embodiment in this invention is a semiconductor devicewhich includes a plurality of gate wirings formed by being extended in afirst direction, a plurality of source wirings extended in a seconddirection which intersects with the gate wirings, a plurality of pixelportions defined by the gate wiring and the source wiring, a gateelectrode formed in each of the pixel portions and extended from thegate wiring, and a switching element including a source electrodeextended from the source wiring. The gate wiring is formed of a firstconductive film and a second conductive film thereover. The sourcewiring is formed of a third conductive film and a fourth conductive filmthereover. The gate electrode is formed of the first conductive film.The source electrode is formed of the third conductive film.

Further, in one embodiment of this invention, the first conductive filmand the third conductive film preferably have a light-transmittingproperty. Furthermore, in one embodiment of this invention, the secondconductive film and the fourth conductive film preferably have alight-shielding property. Furthermore, in one embodiment of thisinvention, the second conductive film and the fourth conductive filmhave higher conductivity than the first conductive film and the thirdconductive film.

Further, in one embodiment of this invention, the second conductive filmis formed of one or a plurality of elements selected from Al, Ti, Cu,Au, Ag, Mo, Ni, Ta, Zr, and Co. Furthermore, in one embodiment of thisinvention, the fourth conductive film is formed of one or a plurality ofelements selected from Al, Ti, Cu, Au, Ag, Mo, Ni, Ta, Zr, and Co.

By employing such a structure, a light-transmitting transistor or alight-transmitting capacitor element can be formed. Therefore, eventhough the transistor or the capacitor element is provided in a pixel, adecrease in an aperture ratio can be suppressed. Further, since a wiringfor connecting the transistor and an element (e.g., another transistor)or a wiring for connecting the capacitor element and an element (e.g.,another capacitor element) is formed by using a material with lowresistivity and high conductivity, the blunting of the waveform of asignal and a voltage drop due to wiring resistance can be suppressed.

Further, one embodiment of this invention is a semiconductor device inwhich the semiconductor film is any one of zinc oxide, titanium oxide,magnesium zinc oxide, cadmium zinc oxide, cadmium oxide, InGaO₃(ZnO)₅,and an In—Ga—Zn—O based amorphous oxide semiconductor.

Further, one embodiment of this invention is a manufacturing method of asemiconductor device, in which a first conductive film and a secondconductive film are sequentially formed over a light-transmittinginsulating substrate, a first resist mask having a portion where astacked layer of the first conductive film and the second conductivefilm remain and a portion where only the first conductive film remains,whose thicknesses are different from each other is formed byphotolithography with a multi-tone mask, the first conductive film andthe second conductive film are etched by using the first resist mask, asecond resist mask is formed by ashing the first resist mask, the secondconductive film is etched by using the second resist mask and part ofthe first conductive film is exposed, a first insulating film is formedso as to cover the insulating substrate, the first conductive film, andthe second conductive film, an island-shaped semiconductor film isformed over the first conductive film with the first insulating filminterposed therebetween, a third conductive film and a fourth conductivefilm are sequentially formed over the insulating film, a third resistmask having a portion where a stacked layer of the third conductive filmand the fourth conductive film remain and a portion where only the firstconductive film remains, whose thicknesses are different from each otheris formed by photolithography with a multi-tone mask, the thirdconductive film and the fourth conductive film are etched by using thethird resist mask, a fourth resist mask is formed by ashing the thirdresist mask, and the fourth conductive film is formed by using thefourth resist mask and part of the third conductive film is exposed.

Further in the conductive layers, a light-transmitting region (a regionwith high light transmittance) and a light-shielding region (a regionwith low light transmittance) can be formed by one mask (reticle) withuse of a multi-tone mask. Accordingly, the light-transmitting region(the region with high light transmittance) and the light-shieldingregion (the region with low light transmittance) can be formed withoutincreasing the number of masks.

Note that semiconductor devices in this specification mean all deviceswhich can function by utilizing semiconductor characteristics, anddisplay devices, semiconductor circuits, and electronic devices are allsemiconductor devices.

According to one embodiment of this invention, the light-transmittingtransistor or the light-transmitting capacitor element can be formed.Therefore, even if the transistor or the capacitor is provided in apixel, aperture ratio can be made high. Further, since a wiring forconnecting the transistor and an element (e.g., another transistor) or awiring for connecting a capacitor element and an element (e.g., anothercapacitor element) can be formed by using a material with lowresistivity and high conductivity, the distortion of the waveform of asignal and a voltage drop due to wiring resistance can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1A is a top view of a semiconductor device according to oneembodiment of this invention and FIG. 1B is a cross-sectional view ofthe semiconductor device of one embodiment in this invention;

FIGS. 2A to 2D are cross-sectional views illustrating a manufacturingmethod of a semiconductor device of one embodiment in this invention;

FIGS. 3A to 3D are cross-sectional views illustrating the manufacturingmethod of the semiconductor device of one embodiment in this invention;

FIGS. 4A to 4D are cross-sectional views illustrating the manufacturingmethod of the semiconductor device of one embodiment in this invention;

FIGS. 5A to 3D are cross-sectional views illustrating the manufacturingmethod of the semiconductor device of one embodiment in this invention;

FIGS. 6A to 6C are cross-sectional views illustrating the manufacturingmethod of the semiconductor device of one embodiment in this invention;

FIGS. 7A to 7C are cross-sectional views illustrating the manufacturingmethod of the semiconductor device of one embodiment in this invention;

FIGS. 8A to 8D are cross-sectional views illustrating the manufacturingmethod of the semiconductor device of one embodiment in this invention;

FIGS. 9A to 9D are cross-sectional views illustrating the manufacturingmethod of the semiconductor device of one embodiment in this invention;

FIG. 10A is a top view of a semiconductor device of one embodiment inthis invention and FIG. 10B is a cross-sectional view of thesemiconductor device of one embodiment in this invention;

FIG. 11A is a top view of a semiconductor device of one embodiment inthis invention and FIG. 11B is a cross-sectional view of thesemiconductor device of one embodiment in this invention;

FIG. 12A is a top view of a semiconductor device of one embodiment inthis invention and FIG. 12B is a cross-sectional view of thesemiconductor device of one embodiment in this invention;

FIGS. 13A-1, 13A-2, 13B-1, and 13B-2 are diagrams for illustrating amulti-tone mask which can be applied to one embodiment in thisinvention;

FIG. 14A is a top view of a display device of one embodiment in thisinvention and FIG. 14B is a cross-sectional view of the display deviceof one embodiment in this invention;

FIGS. 15A to 15C are diagrams each illustrating an electronic devicewhich employs a display device of one embodiment in this invention;

FIG. 16A to 16C are diagrams illustrating an electronic device whichemploys a display device of one embodiment in this invention;

FIG. 17A is a top view of a semiconductor device of one embodiment inthis invention and FIG. 17B is a cross-sectional view of thesemiconductor device of one embodiment in this invention;

FIG. 18A is a top view of a display device of one embodiment in thisinvention and FIG. 18B is a cross-sectional view of the display deviceof one embodiment in this invention; and

FIG. 19 is a cross-sectional view of a semiconductor device of oneembodiment in this invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of this invention will be described withreference to drawings. However, this invention can be implemented invarious forms and it is easily understood by those skilled in the artthat embodiments and details disclosed herein can be variously changedwithout departing from the spirits and scope of this invention.Accordingly, this invention is not construed as being limited to thedescription of the following embodiments. Note that the same referencenumeral is commonly used to denote the same component among thedifferent drawings in the structure of this invention described below.Thus, detailed description of the same portions or portions having asimilar function are omitted.

Embodiment 1

FIG. 1A is a top view illustrating one example of a semiconductor deviceof this embodiment and FIG. 1B is a cross-sectional view of FIG. 1Aalong line A-B.

As shown in FIG. 1A, an element substrate includes a pixel portion whichhas a gate wiring and a storage capacitor line provided in direction 1,a source wiring provided in direction 2 which intersects with the gatewiring and the storage capacitor line, and a transistor around a portionwhere the gate wiring and the source wiring intersect with each other.

In order to increase the aperture ratio of a pixel, a transistor of thisembodiment includes a light-transmitting conductive layer whichfunctions as a gate electrode, a gate insulating film formed over thelight-transmitting conductive layer, a semiconductor layer formed overthe light-transmitting conductive layer which functions as the gateelectrode with the gate insulating film interposed therebetween, andlight-transmitting conductive layers which function as source and drainelectrodes electrically connected to the semiconductor layer.

In this manner, by forming the semiconductor layer and the electrode ofthe transistor by using a light-transmitting substance, the apertureratio of the pixel can be increased. However, when the gate wiringelectrically connected to the gate electrode and the source wiringelectrically connected to the source and drain electrodes are formed byusing a light-transmitting substance, wiring resistance increases,thereby causes an increase in power consumption. Therefore, the gatewiring and the source wiring are formed with a layered structure inwhich a light-transmitting conductive layer and a light-shieldingconductive layer are stacked in this order. As the transistor, eitherone of a top-gate type and a bottom-gate type can be used.

The gate wiring electrically connected to the gate electrode of thetransistor is formed by stacking a light-transmitting conductive layer107 a and a light-shielding conductive layer 110 a in this order, andthe source wiring electrically connected to the source or drainelectrode of the transistor is formed by staking a light-transmittingconductive layer 119 a and a light-shielding layer 122 in this order. Inother words, the gate electrode of the transistor is formed using partof the light-transmitting conductive layer 107 a which is included inthe gate wiring, and the source and drain electrodes are formed usingpart of the light-transmitting conductive layer 119 a which is includedin the source wiring.

By stacking the light-transmitting conductive layer and thelight-shielding conductive layer in this order to form the gate wiringand the source wiring, wiring resistance and power consumption can bereduced. In addition, since the gate wiring and the source wiring areeach formed using the light-shielding conductive layer, a space betweenpixels can be shielded from light. That is, with the gate wiringprovided in a row direction and the source wiring provided in columndirection, the space between the pixels can be shielded from lightwithout using a black matrix.

In the case where the transistor is formed over the gate wiring, thesize of the transistor depends on the width of the gate wiring of thetransistor. However, in this embodiment, since the transistor is formedin a pixel, the size of the transistor can be large. As shown in FIGS.17A and 17B, the transistor which is larger than the width of the gatewiring can be formed. By forming a large transistor, its electricperformance can be adequately high, and a writing time of a signal tothe pixel can be shortened. Accordingly, a display device with highdefinition can be provided.

In addition, the storage capacitor line provided in the direction 1which is the same as that of the gate wiring is formed by stacking alight-transmitting conductive layer and a light-shielding conductivelayer in this order like the gate wiring. A storage capacitor portion isformed in the storage capacitor line. The storage capacitor portionincludes a light-transmitting conductive layer which functions as alower electrode and a light-transmitting conductive layer whichfunctions as an upper electrode, by using an insulating film serving asa gate insulating film as a dielectrics.

In this manner, by forming the storage capacitor portion with thelight-transmitting conductive layer, aperture ratio can be increased. Inaddition, by forming the storage capacitor portion with thelight-transmitting conductive layer, the storage capacitor portion canbe large, so that the potential of a pixel electrode can be easily heldeven when the transistor is turned off. Moreover, feedthrough potentialcan be low.

Moreover, the number of masks necessary for forming an element substratehaving the pixel configuration shown in FIGS. 1A and 1B can be 5. Thatis, a first mask is used for forming the gate wiring and the capacitorwiring, a second mask is for forming a semiconductor layer 113, a thirdmask is for forming the source wiring and the upper electrode of thestorage capacitor portion, a fourth mask is for forming contact holeswhich reach the source wiring and the upper electrode of the storagecapacitor portion and a fifth mask is for forming a pixel electrode 124.

In this manner, in the case of the pixel configuration shown in FIGS. 1Aand 1B, a display device with high aperture ratio can be achieved withthe small number of masks.

Next, one example of a manufacturing process of a semiconductor deviceof this embodiment is shown with reference to cross-sectional views inFIGS. 2A to 2D, FIGS. 3A to 3D, FIGS. 4A to 4D, FIGS. 5A to 5D, FIGS. 6Ato 6C, FIGS. 7A to 7C, FIGS. 8A to 8D, and FIGS. 9A to 9D. Although acase where a multi-tone mask is used is described with reference toFIGS. 2A to 2D, FIGS. 3A to 3D, FIGS. 4A to 4D, FIGS. 5A to 5D, FIGS. 6Ato 6C, FIGS. 7A to 7C, FIGS. 8A to 8D, and FIGS. 9A to 9D, thisembodiment is not limited thereto. Note that FIGS. 2A to 2D, FIGS. 4A to4D, FIGS. 6A to 6C, and FIGS. 8A to 8D are cross-sectional views of FIG.1A along line A-C, and FIGS. 3A to 3D, FIGS. 5A to 5D, FIGS. 7A to 7C,and FIGS. 9A to 9D are cross-sectional views of FIG. 1A along line D-E.FIGS. 2A to 2D, FIGS. 4A to 4D, FIGS. 6A to 6C, and FIGS. 8A to 8Dcorrespond to FIGS. 3A to 3D, FIGS. 5A to 5D, FIGS. 7A to 7C, and FIGS.9A to 9D, respectively. Note that FIGS. 2A to 2D, FIGS. 4A to 4D, andFIGS. 6A to 6C illustrate a source wiring portion 301, a transistorportion 302, a gate wiring portion 303, and a storage capacitor portion304, and FIGS. 3A to 3D, FIGS. 5A to 5D, FIGS. 7A to 7C illustrate thetransistor portion 302 and the gate wiring portion 303.

First, as shown in FIG. 2A and FIG. 3A, a conductive film 102 and aconductive film 103 are stacked over a substrate 101 by sputtering.These steps are consecutively performed, and further sputtering can beconsecutively performed by using a multi-chamber. By consecutivelyforming the conductive film 102 and the conductive film 103, throughputis increased and contamination by an impurity or dust can be suppressed.

The substrate 101 is preferably formed using a material having highlight transmittance. For example, a glass substrate, a plasticsubstrate, an acrylic substrate, a ceramic substrate, or the like can beused.

It is preferable that the light transmittance of the conductive film 102be sufficiently high. Moreover, the light transmittance of theconductive film 102 is preferably higher than that of the conductivefilm 103.

As the conductive film 102, indium tin oxide (ITO), indium tin oxidecontaining silicon oxide (ITSO), organic indium, organic tin, zincoxide, titanium nitride, or the like can be used. Alternatively, indiumzinc oxide (IZO) containing zinc oxide (ZnO), zinc oxide (ZnO), ZnOdoped with gallium (Ga), tin oxide (SnO₂), indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium tin oxide containing titaniumoxide, or the like may be used. Such a material can be used to form theconductive film 102 with a single-layer structure or a layered structureby sputtering. However, in the case of the layered structure, the lighttransmittance of each of a plurality of films is preferably high enough.

The resistivity of the conductive film 103 is preferably low enough andthe conductivity of the conductive film 103 is preferably high enough.In addition, the resistivity of the conductive film 102 is preferablylower than that of the conductive film 103. However, since theconductive film 102 functions as a conductive layer, the resistivity ofthe conductive film 102 is preferably lower than that of an insulatinglayer.

The conductive film 103 can be formed to have a single-layer structureor a layered structure using a metal material such as molybdenum,titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, orscandium, or an alloy material containing the above material as its maincomponent, by sputtering or vacuum evaporation. In addition, in the casewhere the conductive film 103 is formed to have a layered structure, alight-transmitting conductive film may be included in the plurality offilms.

Note that when the conductive film 103 is formed over the conductivefilm 102, both of the films react with each other in some cases. Forexample, when the top surface (a surface which is in contact with theconductive film 103) of the conductive film 102 is formed using ITO andthe bottom surface (a surface which is in contact with the conductivefilm 102) of the conductive film 103 is formed using aluminum, achemical reaction occurs therebetween. Accordingly, in order to avoidthe chemical reaction, a material with a high melting point ispreferably used for the bottom surface (the surface which is in contactwith the conductive film 102) of the conductive film 103. For example,as the material with a high melting point, molybdenum (Mo), titanium(Ti), tungsten (W), neodymium (Nd), or the like can be given. Also, itis preferable to form the conductive film 103 into a multi-layer film byusing a material with high conductivity over a film formed using thematerial with the high melting point. As the material with highconductivity, aluminum (Al), copper (Cu), silver (Ag), or the like canbe given. For example, in the case where the conductive film 103 isformed to have a layered structure, a stacked layer of molybdenum (Mo)as a first layer, aluminum (Al) as a second layer, and molybdenum (Mo)as a third layer, or a stacked layer of molybdenum (Mo) as a firstlayer, aluminum (Al) containing a small amount of neodymium (Nd) as asecond layer, and molybdenum (Mo) as a third layer can be used.

Since the conductive film 102 is formed under the conductive film 103 inthe structure of this embodiment, only the conductive film 103 can beformed using commercial glass provided with ITO (indium tin oxide) bysputtering.

Although not shown, note that silicon oxide, silicon nitride, siliconoxynitride, or the like can be formed as a base film between thesubstrate 101 and the conductive film 102. By forming the base filmbetween the substrate 101 and the light-transmitting conductive film,diffusing of mobile ions, impurities, or the like from the substrate 101into an element can be suppressed, whereby the deterioration in thecharacteristic of the element can be prevented.

Next, as shown in FIG. 2B and FIG. 3B, resist masks 106 a and 106 b areformed over the conductive film 103. The resist masks 106 a and 106 bcan be formed to have regions with different thicknesses by using amulti-tone mask. By using the multi-tone mask, the number of photomasksused and the number of manufacturing steps can be reduced, which ispreferable. In this embodiment, a multi-tone mask can be used in a stepfor forming the pattern of the conductive film 102 and the conductivefilm 103 and a step for forming the light-transmitting conductive layerwhich functions as the gate electrode.

The multi-tone mask is a mask with which exposure can be performed withthe amount of light in a plurality of levels. Typically, exposure isperformed with the amount of light in three levels: an exposure region,a half-exposure region, and a non-exposure region. By using themulti-tone mask, a resist mask with a plurality of thicknesses(typically two thicknesses) can be formed through one exposure step andone development step. Thus, the number of photomasks can be reduced byusing the multi-tone mask.

FIGS. 13A-1 and 13B-1 are cross-sectional views of typical multi-tonemasks. FIG. 13A-1 shows a gray-tone mask 180 and FIG. 13B-1 shows ahalf-tone mask 185.

The gray-tone mask 180 shown in FIG. 13A-1 includes a light-shieldingportion 182 formed using a light-shielding layer on a light-transmittingsubstrate 181 and a diffraction grating portion 183 formed by thepattern of the light-shielding layer.

The diffraction grating portion 183 controls the amount of transmittedlight by using slits, dots, meshes, or the like provided in intervalswhich are equal to or smaller than the limit of the resolution of lightused for exposure. Note that the slits, dots, or meshes may be providedin the diffraction grating portion 183 in periodic intervals ornon-periodic intervals.

As the light-transmitting substrate 181, quartz or the like can be used.The light-shielding layer included in the light-shielding portion 182and the diffraction grating portion 183 may be formed using a metalfilm: preferably chromium, chromium oxide, or the like.

When the gray-tone mask 180 is irradiated with light for exposure, thetransmittance of a region which overlaps with the light-shieldingportion 182 is 0% as shown in FIG. 13A-2 and the transmittance of aregion which is not provided with the light-shielding portion 182 or thediffraction grating portion 183 is 100%. In addition, the transmittanceof the diffraction grating portion 183 is approximately 10 to 70% andcan be adjusted by intervals between slits, dots or meshes in thediffraction grating, or the like.

The half-tone mask 185 shown in FIG. 13B-1 includes asemi-light-transmitting portion 187 and a light-shielding portion 188which are formed using a semi-light-transmitting layer and alight-shielding layer, respectively, over a light-transmitting substrate186.

The semi-light-transmitting portion 187 can be formed by using a layerof MoSiN, MoSi, MoSiO, MoSiON, CrSi, or the like. The light-shieldingportion 188 may be provided by using the same metal film as thelight-shielding layer for the gray-tone mask, preferably, such aschromium or chromium oxide.

When the half-tone mask 185 is irradiated with light for exposure, thetransmittance of a region which overlaps with the light-shieldingportion 188 is 0% as shown in FIG. 13B-2 and the transmittance of aregion which is not provided with the light-shielding portion 188 or thesemi-light-transmitting portion 187 is 100%. In addition, thetransmittance of the semi-light-transmitting portion 187 isapproximately 10 to 70% and can be adjusted by the kind of material usedor the thickness of a film to be formed, or the like.

By performing exposure and development with the use of the multi-tonemask, the resist mask having the regions with different thicknesses canbe formed. In addition, the resist mask with different thicknesses canbe formed.

As shown in FIG. 2B and FIG. 3B, a half-tone mask includessemi-light-transmitting layers 105 a and 105 c and a light-shieldinglayer 105 b on a light-transmitting substrate 104. Accordingly, aportion which is to be the bottom electrode of the storage capacitorportion and a portion which is to be the gate electrode are providedwith a region with a small thickness of the resist mask 106 a and thethin resist mask 106 b, and a portion which is to be the gate wiring isprovided with a region with a large thickness of the resist mask 106 aover the conductive film 103.

Next, as shown in FIG. 2C and FIG. 3C, the conductive films 102 and 103are etched by using the resist masks 106 a and 106 b. By the etching,conductive layers 107 a, 108 a, 107 b, and 108 b can be formed.

Next, as shown in FIG. 2D, and FIG. 3D, the resist masks 106 a and 106 bare ashed by an oxygen plasma. By ashing the resist masks 106 a and 106b by the oxygen plasma, the region with the small thickness of theresist mask 106 a is removed and the light-shielding conductive layerunder the resist mask 106 a is exposed. In addition, the region with alarge thickness of resist mask 106 a becomes small and remains as aresist mask 109. In this manner, by using the resist mask formed usingthe multi-tone mask, a resist mask is not additionally used, so thatsteps can be simplified.

Next, the light-shielding conductive layer 108 a is etched by using theresist mask 109. As a result, part of the conductive layer 108 a isremoved and the conductive layer 107 a is exposed. In addition, theconductive layer 108 a except a portion on which the resist mask 109 isformed is removed. This is because the part of the conductive layer 108a is exposed due to the reduction of the resist mask 106 a in size bythe ashing treatment. Accordingly, the part of the conductive layer 108a, which is not covered with the resist mask 109 is etched at the sametime. Thus, the areas of the conductive layer 108 a and the conductivelayer 107 a are largely different from each other. In other words, thearea of the conductive layer 107 a is larger than that of the conductivelayer 108 a. Alternatively, the conductive layers 108 a and 107 ainclude a region in which the conductive layers 108 a and 107 a overlapwith each other, and a region in which the conductive layers 108 a and107 a do not overlap with each other.

When the light-shielding conductive layer is removed, part of thelight-transmitting conductive layer (for example, a surface portionwhich is in contact with the light-shielding conductive layer) is alsoremoved in some cases. The selectivity of the light-shielding conductivelayer to the light-transmitting conductive layer in etching determineshow much the light-transmitting conductive layer is removed. Therefore,for example, the thickness of the conductive layer 107 a in a regioncovered with the conductive layer 110 a is larger than that of theconductive layer 107 a in a region which is not covered with theconductive layer 110 a in many cases.

In the case where only the light-shielding conductive layer is removedby wet etching while the light-transmitting conductive layer is left, anetching solution with high selectivity of the light-shielding conductivelayer to the light-transmitting conductive layer is used. In the casewhere a stacked layer of molybdenum (Mo) as a first layer, aluminum (Al)as a second layer, and molybdenum (Mo) as a third layer, or a stackedlayer of molybdenum (Mo) as a first layer, aluminum (Al) containing asmall amount of neodymium (Nd) as a second layer, and molybdenum (Mo) asa third layer is used as the light-shielding conductive layer, forexample, a mixed acid of phosphoric acid, nitric acid, acetic acid, andwater can be used for the wet etching. With the use of this mixed acid,a forward tapered shape which is uniform and favorable can be obtained.In this manner, in addition to an improvement in coverage due to atapered shape, high throughput can be obtained while the wet etching isa simple process in which an etching by an etchant, a rinse by purewater, and drying are performed. Thus, wet etching is suitable foretching of the above light-shielding conductive layer.

Next, the resist mask 109 is removed as shown in FIG. 4A and FIG. 5A.

Part of a region in the conductive layers 110 a and 107 a (a regionmainly including the conductive layer 110 a) can function as the gatewiring or part of the gate wiring while another part of the region (aregion mainly including only the conductive layer 107 a) can function asthe gate electrode or part of the gate electrode of the transistor. Itis preferable that a region in which the conductive layers 110 a and 107a overlap with each other function as the gate wiring or the part of thegate wiring because the region includes the conductive layer 110 a whichhas high conductivity in many cases. Alternatively, it is preferablethat the conductive layer 107 a in the region which does not include theconductive layer 110 a function as the gate electrode or the part of thegate electrode of the transistor because the region can transmit lightin some cases.

Accordingly, in the conductive layers 110 a and 107 a, a wiring whichfunctions as the gate electrode, may be considered to be connected to awiring which functions as the gate wiring (or at least one of theconductive layers 110 a and 107 a which functions as the gate wiring).Alternatively, at least one of the conductive layers 110 a and 107 aincluded in the gate wiring may be formed to have a larger area than theother layer included in the gate wiring; part of the region with thelarger area can be considered to function as the gate electrode.Alternatively, the conductive layer 107 a may be formed to have a largerarea than the conductive layer 110 a; part of the region with the largerarea can be considered to function as the gate electrode. That is, thepart of the gate wiring can be considered to function as the gateelectrode or the part of the gate electrode. Alternatively, theconductive layer 110 a that mainly functions as the gate wiring or thepart of the gate wiring can be considered to be formed over theconductive layer 107 a that mainly functions as the gate electrode orthe part of the gate electrode.

Similarly, part of a region in the light-shielding conductive layer andthe conductive layer 107 b (a region mainly including the conductivelayer 110 b) can function as the capacitor wiring or part of thecapacitor wiring, and another part of the region (a region mainlyincluding only the conductive layer 107 b) can function as an electrodeof a capacitor element or part of the electrode of the capacitorelement. It is preferable that a region in which the light-shieldingconductive layer and the conductive layer 107 b overlap with each otherfunction as the capacitor wiring or the part of the capacitor wiringbecause the region includes the light-shielding conductive layer whichhas high conductivity in many cases. Alternatively, it is preferablethat the conductive layer 107 b in the region which does not include thelight-shielding conductive layer function as the electrode of thecapacitor element or the part of the electrode of the capacitor elementbecause the region can transmit light in some cases.

Accordingly, in the light-shielding conductive layer and the conductivelayer 107 b, a wiring which functions as the electrode of the capacitorelement, may be considered to be connected to a wiring which functionsas the capacitor element (or at least one of the light-shieldingconductive layer and the conductive layer 107 b which functions as thecapacitor wiring). Alternatively, at least one of the light-shieldingconductive layer and the conductive layer 107 b included in thecapacitor wiring may be formed to have a larger area than the otherlayer included in the capacitor wiring; part of the region with thelarger area can be considered to function as the electrode of thecapacitor element. Alternatively, the conductive layer 107 b may beformed to have a larger area than the light-shielding conductive layer;part of the region with the larger area can be considered to function asthe electrode of the capacitor element. That is, the part of thecapacitor wiring can be considered to function as the electrode of thecapacitor element or the part of the electrode of the capacitor element.Alternatively, the conductive layer 110 b that mainly functions as thecapacitor wiring or the part of the capacitor wiring can be consideredto be formed over the conductive layer 107 b that mainly functions asthe electrode of the capacitor element or the part of the electrode ofthe capacitor element.

Next, as shown in FIG. 4B and FIG. 5B, an insulating film 111 whichfunctions as a gate insulating film is formed so as to cover thelight-transmitting conductive layer and the light-shielding conductivelayer. After that, a semiconductor film 112 is formed over theinsulating film 111.

The insulating film 111 may be formed to have a single-layer structureor a layered structure including a plurality of films. In the case ofthe layered structure including a plurality of films, it is preferablethat all of the films have sufficiently high transmittance. Similarly,the semiconductor film 112 may be formed to have a single-layerstructure or a layered structure including a plurality of films. In thecase of the layered structure including a plurality of films, it ispreferable that all of the films have sufficiently high transmittance.

The insulating film 111 which covers the light-transmitting conductivelayer and the light-shielding conductive layer is formed to a thicknessof 50 to 500 nm. The insulating film 111 may be formed to have asingle-layer structure of a film containing an oxide of silicon or anitride of silicon, or as a layered structure thereof, by a sputteringmethod or a variety of CVD methods such as a plasma CVD method.Specifically, a film containing silicon oxide (SiOx), a film containingsilicon oxynitride (SiOxNy), or a film containing silicon nitride oxide(SiNxOy) is formed as a single-layer structure, or these films areappropriately stacked to form the insulating film 111.

The insulating film may be formed by oxidizing or nitriding the surfaceof the light-transmitting conductive layer or the light-shieldingconductive layer through a high density plasma treatment in anatmosphere containing oxygen, nitrogen, or oxygen and nitrogen. Theinsulating film formed through a high density plasma treatment hasexcellent uniformity in its film thickness, film quality, and the likeand the film can be formed to be dense. As an atmosphere containingoxygen, a mixed gas of oxygen (O₂), nitrogen dioxide (NO₂) or dinitrogenmonoxide (N₂O), and a rare gas; or a mixed gas of oxygen (O₂), nitrogendioxide (NO₂) or dinitrogen monoxide (N₂O), a rare gas, and hydrogen(H₂); can be used. As an atmosphere containing nitrogen, a mixed gas ofnitrogen (N₂) or ammonia (NH₂) and a rare gas, or a mixed gas ofnitrogen (N₂) or ammonia (NH₃), a rare gas, and hydrogen (Ha) can beused. The surfaces of the light-transmitting conductive layer and thelight-shielding conductive layer can be oxidized or nitrided by oxygenradicals (including OH radicals in some cases) or nitrogen radicals(including NH radicals in some cases) generated by high density plasma.

In the case where the insulating film 111 is formed by the high densityplasma treatment, the insulating film 111 is formed so as to have athickness of 1 to 20 nm, typically 5 to 10 nm, and cover thelight-transmitting conductive layer and the light-shielding conductivelayer. Since the reaction which occurs in this case is a solid-phasereaction, an interface state density between the insulating film 111 andthe light-transmitting conductive layer and the light-shieldingconductive layer can be extremely low. Since the light-transmittingconductive layer and the light-shielding conductive layer are directlyoxidized or nitrided, the thickness of the formed insulating film 111may be uniform. Consequently, by solid-phase oxidation of the surface ofthe electrode by the high density plasma treatment shown here, aninsulating film with favorable uniformity and low interface statedensity can be formed. Here, an oxide of an element selected fromtantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), chromium(Cr), niobium (Nb), or the like; or an oxide of an alloy material or acompound material mainly containing the element functions as theinsulating film 111.

For the insulating film 111, just an insulating film formed by the highdensity plasma treatment may be used, or at least one insulating film ofsilicon oxide, silicon nitride containing oxygen, silicon oxidecontaining nitrogen, or the like may be additionally stacked over theinsulating film by a CVD method utilizing plasma or heat reaction.Either way, transistors in each of which a gate insulating film ispartly or entirely an insulating film formed by the high density plasmacan be made to have little variations in characteristic.

The insulating film 11 may use the following which have favorablecompatibility with the oxide semiconductor film: alumina (Al₂O₃),aluminum nitride (AlN), titanium oxide (TiO₂), zirconia (ZrO₂), lithiumoxide (Li₂O), potassium oxide (K₂O), sodium oxide (Na₂O), indium oxide(In₂O₃), yttrium oxide (Y₂O₃), or calcium zirconate (CaZrO₃); or amaterial including at least two thereof. The gate insulating film 111may be formed as a single layer or as stacked layers of two or morelayers.

The insulating film 111 is preferably formed using a light-transmittingmaterial or a material with high light transmittance. Also, theconductive layer 107 a, the conductive layer 107 b, or the semiconductorfilm 112 are preferably formed using a light-transmitting material or amaterial with high light transmittance. Therefore, comparing their lighttransmittance, it is preferable that the insulating film 111 have higherlight transmittance than or approximately the same transmittance as theconductive layer 107 a, the conductive layer 107 b, or the semiconductorfilm 112. This is because the insulating film 111 is formed to have alarge area in some cases and higher transmittance is preferable in orderto increase the use efficiency of light.

Since the insulating film 111 preferably functions as an insulator, theinsulating film 111 preferably has a resistivity that is appropriate forthe insulator. On the other hand, the conductive layers 107 a and 107 bpreferably function as conductors, and the semiconductor film 112preferably functions as a semiconductor. Therefore, the insulating film111 preferably has higher resistivity than the conductive layer 107 a,the conductive layer 107 b, the conductive layers 110 a and 110 b, andthe semiconductor film 112. The insulating film 111 with a highresistivity is preferable because the conductors can be electricallyinsulated from each other, whereby the leakage of current can besuppressed and a circuit can operate with higher performance.

Next, the semiconductor film 112 is formed over the insulating film 111.The semiconductor film 112 is preferably formed using alight-transmitting material or a material with high light transmittance.The semiconductor film 112 can be formed by using an oxidesemiconductor. For the oxide semiconductor, zinc oxide (ZnO) in anamorphous state, a polycrystalline state, or a microcrystalline state inwhich both amorphous and polycrystalline states exist, to which one typeor a plurality of types of impurity elements selected from the followingis added can be used: a Group 1 element (for example, lithium (Li),sodium (Na), kalium (K), rubidium (Rb), or cesium (Cs)), a Group 13element (for example, boron (B), gallium (Ga), indium (In), or thallium(Tl)), a Group 14 element (for example, carbon (C), silicon (Si),germanium (Ge), tin (Sn), or lead (Pb)), a Group 15 element (forexample, nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), orbismuth (Bi)), a Group 17 element (for example, fluorine (F), chlorine(CI), bromine (Br), or iodine (I)), or the like. Alternatively, zincoxide (ZnO) in an amorphous state, a polycrystalline state, or amicrocrystalline state in which both amorphous and polycrystallinestates exist, to which any impurity element is not added can also beused. Further, any of the following can also be used: InGaO₃(ZnO)₅,magnesium zinc oxide (Mg_(x)Zn_(1-x)O), cadmium zinc oxide(Cd_(x)Zn_(1-x)O), cadmium oxide (CdO), or an In—Ga—Zn—O based amorphousoxide semiconductor (a-IGZO). The semiconductor film 112 is formed to athickness of 25 to 200 nm (preferably 30 to 150 nm) by a sputteringmethod under conditions of a pressure of 0.4 Pa and a flow rate ofAr(argon):O₂=50:5 (sccm), and then subsequently etching the film usinghydrofluoric acid diluted to 0.05% into a desired pattern. Compared to asemiconductor film using an amorphous silicon film, the semiconductorfilm 112 does not need to be formed under high vacuum since there is noconcern for oxidation, and is inexpensive as a process. Note that sincean oxide semiconductor film containing zinc oxide is resistant againstplasma, a plasma CVD (also called PCVD or PECVD) method may be used toform the film. Among CVD methods, the plasma CVD method in particularuses a simple device, and has favorable productivity.

Moreover, nitrogen may be added to the foregoing oxide semiconductor. Byadding nitrogen, nitrogen works as an acceptor impurity when the oxidesemiconductor film shows an n-type semiconductor property. Consequently,a threshold voltage of a transistor manufactured using an oxidesemiconductor film to which nitrogen is added can be controlled. WhenZnO is used for the oxide semiconductor, it is favorable that nitrogenbe added (doped) to ZnO. ZnO normally shows an n-type semiconductorproperty. By adding nitrogen, since nitrogen works as an acceptor withrespect to ZnO, a threshold voltage can be controlled as a result. Inthe case where the oxide semiconductor film has an n-type conductivityas it is, an impurity imparting p-type conductivity may be added to aportion of the oxide semiconductor film, in which a channel is to beformed, so that the conductivity type of the portion may be controlledso as to be closer to an i-type (intrinsic semiconductor) as much aspossible.

A thermal treatment may be performed on the semiconductor film 112. Byperforming a thermal treatment on the semiconductor film 112, thecrystallinity in the semiconductor 112 may be increased. Thecrystallization of the semiconductor film 112 may be performed at leastin a channel formation region of the transistor. By increasing thecrystallinity of the channel formation region of the transistor,characteristics of the transistor can be improved.

As the thermal treatment, an RTA (rapid thermal anneal) apparatus or anLRTA (lamp rapid thermal anneal) apparatus which uses a halogen lamp ora lamp for heating can be employed. The LRTA apparatus can use lightwith a wavelength in an infrared rays range, a visible light range, oran ultra violet range. In the case of the LRTA apparatus, heating isperformed at 250 to 570° C. (preferably 300 to 400° C., more preferably300 to 350° C.) for 1 minute to 1 hour, preferably 10 to 30 minutes.LRTA is performed with radiation from one type or a plurality of typesof lamps selected from a halogen lamp, a metal halide lamp, a xenon arclamp, a carbon arc lamp, a high pressure sodium lamp, and a highpressure mercury lamp.

Note that instead of LRTA, a heating treatment may be performed by laserlight irradiation, and for example, laser light of an infrared lightlaser, a visible light laser, an ultraviolet laser, or the like may beused. Alternatively, LRTA and laser light irradiation may be combined toselectively improve crystallinity of the oxide semiconductor film. Whenlaser irradiation is performed, a continuous wave laser beam (CW laserbeam) or a pulsed laser beam (pulse laser beam) can be used. As thelaser beam, a beam emitted from one or plural kinds of a gas laser suchas an Ar laser, a Kr laser, or an excimer laser; a laser using, as amedium, single crystalline YAG, YVO₄, forsterite (Mg₂SiO₄), YAlO₃, orGdVO₄ or polycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, or GdVO₄doped with one or more of Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta as adopant; a glass laser; a ruby laser; an alexandrite laser; a Ti:sapphire laser; a copper vapor laser; and a gold vapor laser, can beused. By emitting a laser beam from the fundamental harmonic of such alaser beam or the second harmonic to the fourth harmonic of thefundamental harmonic of the laser beam, crystallinity can be made to befavorable. Note that it is preferable to use laser light having largerenergy than a band gap of the oxide semiconductor film. For example,laser light emitted from a KrF, ArF, XeCl, or an XeF excimer laseroscillator may be used.

The semiconductor film 112 is preferably formed using alight-transmitting material or a material with high light transmittance.Also, the conductive layer 107 a and the conductive layer 107 b arepreferably formed using a light-transmitting material or a material withhigh light transmittance. Therefore, comparing their lighttransmittance, it is preferable that the conductive layer 107 a and theconductive layer 107 b have higher light transmittance than orapproximately the same transmittance as the semiconductor film 112. Thisis because the conductive layer 107 a and the conductive layer 107 b areformed to have large areas in some cases and higher transmittance ispreferable in order to increase the use efficiency of light.

Although the semiconductor film 112 is preferably formed using alight-transmitting material or a material with high light transmittance,this embodiment is not limited thereto. Even if light transmittance islow, any material can be used as long as the material can transmitlight. For example, the semiconductor film 112 can include silicon (Si)or germanium (Ge). Further, the semiconductor film 112 preferably has atleast any one of crystalline states selected from a single crystal(mono-crystalline) state, polycrystalline state, amorphous state, andmicrocrystalline (nano-crystalline, semi-amorphous) state. The amorphousstate has an advantage in that the semiconductor film 112 may be formedat a low manufacturing temperature, a large semiconductor device ordisplay device can be formed, and a substrate whose melting point islower than that of glass can be used, or the like, which is preferable.

Since the semiconductor film 112 preferably functions as thesemiconductor, the semiconductor film 112 preferably has a resistivitythat is appropriate for the semiconductor. On the other hand, theconductive layers 107 a and 107 b preferably function as conductors.Therefore, the semiconductor film 112 preferably has higher resistivitythan the conductive layer 107 a and the conductive layer 107 b.

Next, a resist mask (not shown) is formed over the semiconductor film112 by a photolithography method, and then etching is performed by usingthe resist mask to form a semiconductor layer 113 (also referred to asan island-shaped semiconductor layer) which is processed into a desiredshape, as shown in FIG. 4C and FIG. 5C. For the etching, hydrofluoricacid diluted to 0.05%, hydrochloric acid, or the like can be used.

The semiconductor layer 113 can function as a semiconductor layer(active layer) of the transistor or part of the semiconductor layer(active layer) of the transistor. Alternatively, the semiconductor layer113 can function as a MOS capacitor or part of the MOS capacitor.Alternatively, the semiconductor layer 113 can function as a film forreducing parasitic capacitance at the intersection portion of wirings.Although not shown, a semiconductor layer containing an impurity elementimparting one conductivity type for forming source and drain regions inthe semiconductor layer 113 may be formed.

Next, as shown in FIG. 4D and FIG. 5D, a conductive film 114 and aconductive film 115 are formed so as to be stacked and cover thesemiconductor 113 and the insulating film 111 by a sputtering method.These steps are consecutively performed, and further, sputtering can beconsecutively performed by using a multi-chamber. By consecutivelyforming the conductive film 114 and the conductive film 115, throughputis increased and contamination by an impurity or dust can be suppressed.

It is preferable that the light transmittance of the conductive film 114be sufficiently high. Moreover, it is preferable that the lighttransmittance of the conductive film 114 be higher than that of theconductive film 115.

As the conductive film 114, indium tin oxide (ITO), indium tin oxidecontaining silicon oxide (ITSO), organic indium, organic tin, zincoxide, titanium nitride, or the like can be used. Alternatively, indiumzinc oxide (IZO) containing zinc oxide (ZnO), ZnO doped with gallium(Ga), tin oxide (SnO₂), indium oxide containing tungsten oxide, indiumzinc oxide containing tungsten oxide, indium oxide containing titaniumoxide, indium tin oxide containing titanium oxide, or the like may beused. Such a material can be used for forming the conductive film 114with a single-layer structure or a layered structure by sputtering.However, in the case of the layered structure, the light transmittanceof each of a plurality of films is preferably high enough.

The conductive film 114 is preferably formed using a materialapproximately the same as that used for the conductive film 102.Approximately the same material is a material having the same element ofa main component of the material used for the conductive film 102. Interms of impurities, the kinds and the concentration of elementscontained are different in some cases. In this manner, when thelight-transmitting conductive film is formed using approximately thesame material by sputtering or evaporation, there is an advantage inthat the material can be shared between the conductive films 102 and114. When the material can be shared, the same manufacturing apparatuscan be used, manufacturing steps can proceed smoothly, and throughputcan be improved, whereby cost cut can be achieved.

The resistivity of the conductive film 115 is preferably low enough andthe conductivity of the conductive film 11 is preferably high enough. Inaddition, the resistivity of the conductive film 114 is preferablyhigher than that of the conductive film 115. However, since theconductive film 114 functions as a conductive layer, the resistivity ofthe conductive film 114 is preferably lower than that of the insulatinglayer.

The conductive film 115 can be formed to have a single-layer structureor a layered structure using a metal material such as molybdenum,titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, orscandium, or an alloy material containing the above material as its maincomponent, by sputtering or vacuum evaporation. In addition, in the casewhere the conductive film 115 is formed to have a layered structure, alight-transmitting conductive film may be included in the plurality offilms.

Moreover, the conductive film 115 is preferably formed using a materialdifferent from that used for the conductive film 103. Alternatively, theconductive film 115 is preferably formed to have a layered structurewhich is different from that of the light-shielding conductive film.This is because, in manufacturing steps, temperatures applied on theconductive film 115 and the conductive film 103 are different from eachother in many cases. In general, the conductive film 103 tends to have ahigher temperature. Accordingly, the conductive film 103 is preferablyformed using a material or a layered structure with a higher meltingpoint. Alternatively, the conductive film 103 is preferably formed usinga material or a layered structure in which hillock is less likely tooccur. Alternatively, since the conductive film 115 is included in asignal line through which a video signal is supplied in some cases, theconductive film 115 is preferably formed using a material or a layeredstructure having lower wiring resistance than the conductive film 103.

Note that when the conductive film 115 is formed over the conductivefilm 114, both of the films react with each other in some cases. Forexample, when the top surface (a surface which is in contact with theconductive film 115) of the conductive film 114 is formed using ITO andthe bottom surface (a surface which is in contact with the conductivefilm 114) of the conductive film 115 is formed using aluminum, achemical reaction occurs. Accordingly, in order to avoid the chemicalreaction, a material with a high melting point is preferably used forthe bottom surface (the surface which is in contact with the conductivefilm 114) of the conductive film 115. For example, as the material witha high melting point, molybdenum (Mo), titanium (Ti), tungsten (W),neodymium (Nd), or the like can be given. Also, it is preferable to formthe conductive film 115 into a multi-layer film by using a material withhigh conductivity over a film formed using the material with the highmelting point. As the material with high conductivity, aluminum (Al),copper (Cu), silver (Ag), or the like can be given. Such materials havea light-shielding property and reflectivity.

Next, as shown in FIG. 6A and FIG. 7A, resist masks 118 a to 118 c areformed over the conductive film 115. The resist masks 118 a to 118 c canbe formed to have regions with different thicknesses by using amulti-tone mask.

As shown in FIG. 6A and FIG. 7A, a half-tone mask includessemi-light-transmitting layers 117 b to 117 d and a light-shieldinglayer 117 a on a light-transmitting substrate 116. Accordingly, over theconductive film 115, thin resist masks are formed on portions which areto be an upper electrode of the storage capacitor portion and source anddrain electrodes, and a thick resist mask is formed on a portion whichis to be a source wiring.

Next, as shown in FIG. 6B and FIG. 7B, the conductive films 114 and 115are etched by using the resist masks 118 a to 118 c. By the etching,conductive layers 119 a, 119 b, 119 c, 120 a, 120 b, and 120 c can beformed.

Here, by etching the semiconductor layer 113 with diluted hydrofluoricacid, part of a channel can be etched.

Next, as shown in FIG. 6C and FIG. 7C, the resist masks 118 a to 118 areashed by an oxygen plasma. By ashing the resist masks 118 a to 118 c bythe oxygen plasma, the resist masks 118 b and 118 c are removed and theconductive layers 120 b and 120 c under the resist masks 118 b and 118 care exposed. In addition, the resist mask 118 a becomes small andremains as a resist mask 121. In this manner, by using the resist maskformed using a multi-tone mask, a resist mask is not additionally used,so that steps can be simplified.

Next, as shown in FIG. 8A and FIG. 9A, the light-shielding conductivelayer is etched by using the resist mask 121. As a result, part of theconductive layer 120 a and the conductive layer 120 c are removed andthe conductive layers 119 b and 119 c are exposed. In addition, theconductive layers 119 a and 120 a except a portion on which the resistmask 121 is formed is removed. This is because the conductive layers 120a is exposed due to the reduction of the resist mask 118 a in size bythe ashing treatment. Accordingly, the part of the light-shieldingconductive layer 120 a, which is not covered with the resist mask 121 isetched at the same time. Thus, the areas of the conductive layer 122 andthe conductive layer 119 a are largely different. In other words, thearea of the conductive layer 119 a is larger than that of the conductivelayer 122. Alternatively, the conductive layers 122 and 119 a include aregion in which the conductive layers 122 and 119 a overlap with eachother, and a region in which the conductive layers 122 and 119 a do notoverlap with each other.

When the light-shielding conductive layer is removed, part of thelight-transmitting conductive layer (for example, a surface portionwhich is in contact with the light-shielding conductive layer) is alsoremoved in some cases. The selectivity of the light-shielding conductivelayer to the light-transmitting conductive layer in etching determineshow much the light-transmitting conductive layer is removed. Therefore,for example, the thickness of the conductive layer 119 a in a regioncovered with the conductive layer 122 is larger than that of theconductive layer 119 a in a region which is not covered with theconductive layer 122 in many cases.

Note that part of a region in the conductive layers 122 and 119 a (aregion mainly including the conductive layer 122) can function as thesource wiring or part of the source wiring while another part of theregion (a region mainly including only the conductive layer 119 a) canfunction as the source electrode or part of the source electrode of thetransistor. It is preferable that a region in which the conductivelayers 122 and 119 a overlap with each other function as the sourcewiring or the part of the source wiring because the region includes theconductive layer 122 which has high conductivity in many cases.Alternatively, it is preferable that the conductive layer 119 a in theregion which does not include the conductive layer 122 function as thesource electrode or the part of the source electrode of the transistorbecause the region can transmit light in some cases.

Accordingly, in the conductive layers 122 and 119 a, a wiring whichfunctions as the source electrode, may be considered to be connected toa wiring which functions as the source wiring (or at least one of theconductive layers 122 and 119 a which functions as the source wiring).Alternatively, at least one of the conductive layers 122 and 119 aincluded in the source wiring may be formed to have a larger area thanthe other layer included in the source wiring; part of the region withthe larger area can be considered to function as the source electrode.Alternatively, the conductive layer 119 a may be formed to have a largerarea than the conductive layer 122; part of the region with the largerarea can be considered to function as the source electrode. That is, thepart of the source wiring can be considered to function as the sourceelectrode or the part of the source electrode. Alternatively, theconductive layer 122 that mainly functions as the source wiring or thepart of the source wiring can be considered to be formed over theconductive layer 119 a that mainly functions as the source electrode orthe part of the source electrode.

Here, as for the source electrode, since source and drain are switchedto each other depending on the level of voltage, the polarity of atransistor, or the like, source can be drain.

Moreover, part of a region in the light-shielding conductive layer andthe conductive layer 119 c (a region mainly including thelight-shielding conductive layer) can function as the capacitor wiringor part of the capacitor wiring, and another part of the region (aregion mainly including only the conductive layer 119 c) can function asan electrode of a capacitor element or part of the electrode of thecapacitor element. It is preferable that a region in which thelight-shielding conductive layer and the conductive layer 119 c overlapwith each other function as the capacitor wiring or the part of thecapacitor wiring because the region includes the light-shieldingconductive layer which has high conductivity in many cases.Alternatively, it is preferable that the conductive layer 119 c in theregion which does not include the light-shielding conductive layerfunction as the electrode of the capacitor element or the part of theelectrode of the capacitor element because the region can transmit lightin some cases.

Accordingly, in the light-shielding conductive layer and the conductivelayer 119 c, a wiring which functions as the electrode of the capacitorelement, may be considered to be connected to a wiring which functionsas the capacitor element (or at least one of the light-shieldingconductive layer and the conductive layer 119 c which functions as thecapacitor wiring). Alternatively, at least one of the light-shieldingconductive layer and the conductive layer 119 c included in thecapacitor wiring may be formed to have a larger area than the otherlayer included in the capacitor wiring; part of the region with thelarger area can be considered to function as the electrode of thecapacitor element. Alternatively, the conductive layer 119 c may beformed to have a larger area than the light-shielding conductive layer;part of the region with the larger area can be considered to function asthe electrode of the capacitor element. That is, the part of thecapacitor wiring can be considered to function as the electrode of thecapacitor element or the part of the electrode of the capacitor element.Alternatively, the conductive layer 110 b that mainly functions as thecapacitor wiring or the part of the capacitor wiring can be consideredto be formed over the conductive layer 119 c that mainly functions asthe electrode of the capacitor element or the part of the electrode ofthe capacitor element.

Next, as shown in FIG. 8C and FIG. 9C, the resist mask 121 is removed.In this manner, a transistor 130 and a capacitor element 131 can beformed into light-transmitting elements.

Since FIG. 9B is a cross-sectional view which is turned perpendicularlyto a direction in which the source and drain electrodes are formed, thesource and drain electrodes are not shown.

Next, as shown in FIG. 8B and FIG. 9B, an insulating film 123 is formed.The insulating film 123 may be formed to have a single-layer structureor a layered structure. In the case of the layered structure, the lighttransmittance of each of films is preferably high enough. The insulatingfilm 123 functions as an insulating film which protects the transistorfrom an impurity or the like. In addition, the insulating film 123 canfunction as an insulating film for smoothing unevenness due to thetransistor, the capacitor element, the wiring, and the like andflattening the surface on which the transistor, the capacitor element,the wiring, and the like are formed. In other words, the insulating film123 can function as a flattening film.

In specific, since the transistor 130 and the capacitor element 131 canbe formed as the light-transmitting elements, it is advantageous toflatten a top portion where these elements are formed by smoothingunevenness due to these elements or the wiring and the like in order touse the region where these elements are formed as an opening region.

The insulating film 123 is preferably formed using a film containingsilicon nitride. A silicon nitride film is preferable because it hashigh effect of blocking impurities. Alternatively, the insulating film123 is preferably formed using a film containing an organic material. Asan example of the organic material, acrylic, polyimide, polyamide, orthe like is preferable. Such organic materials are preferable in termsof a high function of flattening unevenness. Accordingly, in the casewhere the insulating film 123 is formed to have a layered structure of asilicon nitride film and a film of an organic material, it is preferableto provide the silicon nitride film and the film of the organic nitridein the lower side and in the upper side, respectively.

Note that the insulating film 123 can function as a color filter. Byproviding a color filter over the substrate 101, a counter substratedoes not need to be provided with a color filter. Therefore, a marginfor adjusting the position of two substrates is not necessary, wherebymanufacturing of a panel can be made simple.

Next, pan of the insulating film 123 or part of the insulating films 123and 111 is removed to form a contact hole.

Next, as shown in FIGS. 8D and 9D, a conductive film is formed over theinsulating film 123 and in the contact hole. Then, part of theconductive film is etched to form conductive films 124 a and 124 b. Theconductive film may be formed to have a single-layer structure or alayered structure. In the case of the layered structure, the lighttransmittance of each of films is preferably high enough.

The conductive films 124 a and 124 b can function as pixel electrodes.Alternatively, the conductive films 124 a and 124 b can function as theelectrodes of the capacitor element. Therefore, it is preferable thatthe conductive films 124 a and 124 b be formed using alight-transmitting material or a material with high light transmittance.

The conductive films 124 a and 124 b can connect the source wiring, thesource electrode, the gate wiring, the gate electrode, the pixelelectrode, the capacitor wiring, the electrode of the capacitor element,and the like to each other through the contact hole. Therefore, theconductive films 124 a and 124 b can function as a wiring for connectingconductors.

It is preferable to form the conductive films 124 a and 124 b and theconductive film 102 by using approximately the same material.Alternatively, it is preferable to form the conductive films 124 a and124 b and the conductive film 114 by using approximately the samematerial. In this manner, when the light-transmitting conductive film isformed using approximately the same material by sputtering orevaporation, there is an advantage in that the material can be sharedbetween the conductive films. When the material can be shared, the samemanufacturing apparatus can be used, manufacturing steps can proceedsmoothly, and throughput can be improved, whereby cost cut can beachieved.

Although a manufacturing method of a channel-etched transistor isdescribed in this embodiment, one embodiment of this invention is notlimited thereto and a channel-protective transistor can also bemanufactured, One example of a cross-sectional view of achannel-protective transistor is shown in FIG. 19. Thechannel-protective transistor can be formed through the same manner asthe channel-etched transistor up to the steps in FIG. 4A and FIG. 5A.Next, in FIG. 4B and FIG. 5B, a protective film 130 is formed after thesemiconductor film 112 is formed. As the protective film 132, siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide, orthe like can be used as appropriate. Next, a resist mask is formed overthe protective film 132 and the protective film 132 is processed into adesired shape by etching to form a channel protective layer. After that,the same manufacturing step as the channel-etched transistor may beperformed from FIG. 4C and FIG. 5C except for the step of removing partof the channel.

Through this, the light-transmitting transistor or thelight-transmitting capacitor element can be formed by employing oneembodiment of this invention. Therefore, even if the transistor or thecapacitor element is provided in a pixel, aperture ratio can be madehigh. Further, since a wiring for connecting the transistor and anelement (e.g., another transistor) or a wiring for connecting acapacitor element and an element (e.g., another capacitor element) canbe formed by using a material with low resistivity and highconductivity, the distortion of the waveform of a signal and a voltagedrop due to wiring resistance can be reduced.

Next, another example of an element substrate which is different fromthat in FIGS. 1A and 1B will be described with reference to FIGS. 10Aand 10B. FIG. 10A is a top view of a semiconductor device of thisembodiment and FIG. 10B is a cross-sectional view thereof along line F-GFIGS. 10A and 10B are different from FIGS. 1A and 1B in that the area ofthe lower electrode (a conductive layer 107 c) of a storage capacitorportion is large and an upper electrode of the storage capacitor portionis the pixel electrode 124. The size of the storage capacitor portion ispreferably larger than pixel pitch by 70% or more or 80% or more.Hereinafter, since the structure except for the storage capacitorportion and the storage capacitor wiring in FIGS. 10A and 10B is thesame as that in FIGS. 1A and 1B, the detailed description thereof isskipped.

By employing such a structure, transmittance can be increased becausethe upper electrode of the storage capacitor portion does not need to beformed in forming the source wiring and the source and drain electrodes.In addition, the large storage capacitor portion with high transmittancecan be formed. By forming the large storage capacitor portion, even ifthe transistor is turned off, a potential of the pixel electrode iseasily stored. Moreover, feedthrough potential can be low. Further, evenif the large storage capacitor portion is formed, aperture ratio can bemade high and power consumption can be reduced. Furthermore, since theinsulating film has two layers, interlayer short-circuiting due to apinhole or the like generated in the insulating film can be prevented.Furthermore, the unevenness of the capacitor wiring can be smoothed anddisorder of the alignment of liquid crystals can be suppressed.

Next, another example of an element substrate which is different fromthat in FIGS. 1A and 1B will be described with reference to FIGS. 11Aand 11B. FIG. 11A is a top view of a semiconductor device of thisembodiment and FIG. 11B is a cross-sectional view thereof along lineH-I. FIGS. 11A and 11B are different from FIGS. 1A and 1B in that alower electrode (a conductive layer 107 d) of the storage capacitorportion is large, a capacitor wiring is formed by stacking alight-transmitting conductive layer and a light-shielding conductivelayer in this order, and an upper electrode (a conductive layer 119 d)of the storage capacitor portion is large. The size of the storagecapacitor portion is preferably larger than pixel pitch by 70% or moreor 80% or more. Hereinafter, since the structure except for the storagecapacitor portion in FIGS. 11A and 11B is the same as that in FIGS. 1Aand 1B, the detailed description thereof is skipped.

By employing such a structure, the blunting of the waveform of a signaland a voltage drop due to wiring resistance can be suppressed becausethe capacitor wiring can be formed by using a material with lowresistivity and high conductivity. In addition, even if disorder of thealignment of liquid crystals is caused by unevenness due to the contacthole in the pixel electrode, the leakage of light can be prevented bythe light-shielding conductive layer in the capacitor wiring. Further,by forming the large storage capacitor, even if the transistor is turnedoff, a potential of the pixel electrode is easily stored. Moreover,feedthrough potential can be low. Further, even if the large storagecapacitor is formed, aperture ratio can be made high and powerconsumption can be reduced.

Next, another example of an element substrate which is different fromthat in FIGS. 1A and 1B will be described with reference to FIGS. 12Aand 12B. FIG. 12A is a top view of a semiconductor device of thisembodiment and FIG. 12B is a cross-sectional view thereof along lineJ-K. FIGS. 12A and 12B are different from FIGS. 1A and 1B in that thelight-transmitting conductive layer 107 c which functions as the lowerelectrode of the storage capacitor portion is large and thelight-transmitting conductive layer 119 e which functions as the upperelectrode of the storage capacitor portion is large. The size of thestorage capacitor portion is preferably larger than pixel pitch by 70%or more or 80% or more. Hereinafter, since the structure except thestorage capacitor portion in FIGS. 12A and 12B is the same as that inFIGS. 1A and 1B, the detailed description thereof is skipped.

By employing such a structure, the large storage capacitor with hightransmittance can be formed. By forming the large storage capacitor,even if the transistor is turned off, a potential of the pixel electrodeis easily stored. Moreover, feedthrough potential can be low. Further,even if the large storage capacitor is formed, aperture ratio can bemade high and power consumption can be reduced.

Next, the appearance and cross section of a display device of thisembodiment will be described with reference to FIGS. 14A and 14B. FIG.14A is a top view of a liquid crystal display device in which a thinfilm transistor 4010 including a semiconductor layer and a liquidcrystal element 4013 that are formed over a first substrate 4001 aresealed with a sealant 4005 between the first substrate 4001 and a secondsubstrate 4006. FIG. 14B is a cross-sectional view taken along line A-A′of FIG. 14A.

A sealant 4005 is provided so as to surround a pixel portion 4002 and ascanning line driver circuit 4004 which are provided over a firstsubstrate 4001. A second substrate 4006 is provided over the pixelportion 4002 and the scanning line driver circuit 4004. Therefore, thepixel portion 4002 and the scanning line driver circuit 4004 are sealed,together with liquid crystal 4008, between the first substrate 4001 andthe second substrate 4006 with the sealant 4005. A signal line drivercircuit 4003 formed over a substrate, which is prepared separately,using a polycrystalline semiconductor film is mounted at a regiondifferent from the region surrounded by the sealant 4005 over the firstsubstrate 4001. Note that although this embodiment will explain anexample of attaching the signal line driver circuit 4003 including athin film transistor formed using a polycrystalline semiconductor filmto the first substrate 4001, a signal line driver circuit including athin film transistor, which is formed using a single-crystallinesemiconductor film, may be attached to the first substrate 4001. FIGS.14A and 14B exemplifies a thin film transistor 4009 formed using apolycrystalline semiconductor film, which is included in the signal linedriver circuit 4003.

The pixel portion 4002 and the scanning line driver circuit 4004 formedover the first substrate 4001 each include a plurality of thin filmtransistors, and the thin film transistor 4010 included in the pixelportion 4002 is illustrated as an example in FIG. 14B. The thin filmtransistor 4010 corresponds to a thin film transistor using asemiconductor film. Although the storage capacitor portion is not shownin the pixel portion 4002, the storage capacitor portion shown in FIGS.1A and 1B, FIGS. 10A and 10B, FIGS. 11A and 11B, and FIGS. 12A and 12Bcan be formed.

As described above, the gate wiring which is electrically connected tothe gate electrode of the transistor is formed by stacking thelight-transmitting conductive layer and the light-shielding conductivelayer in this order, and the source wiring which is electricallyconnected to the source and drain electrodes of the transistor is formedby stacking the light-transmitting conductive layer and thelight-shielding conductive layer in this order. That is, the gateelectrode of the transistor is formed using part of thelight-transmitting conductive layer included in the gate wiring and thesource and drain electrodes are formed using part of thelight-transmitting conductive layer included in the source wiring.

By stacking the light-transmitting conductive layer and thelight-shielding conductive layer in this order to form the gate wiringand the source wiring, wiring resistance and power consumption can bereduced. In addition, since the gate wiring and the source wiring areeach formed using the light-shielding conductive layer, a space betweenpixels can be shielded from light. Accordingly, with the gate wiringprovided in a row direction and the source wiring provided in a columndirection, the space between the pixels can be shielded from lightwithout using a black matrix.

In this manner, by forming the storage capacitor portion with thelight-transmitting conductive layer, aperture ratio can be increased. Inaddition, by forming the storage capacitor portion with thelight-transmitting conductive layer, the storage capacitor portion canbe large, so that the potential of a pixel electrode can be easilystored even when the transistor is turned off.

Reference numeral 4013 denotes a liquid crystal element, and a pixelelectrode 4030 included in the liquid crystal element 4013 iselectrically connected to the thin film transistor 4010 through a wiring4040. A counter electrode 4031 of the liquid crystal element 4013 isformed on the second substrate 4006. The liquid crystal element 4013corresponds to a portion where the pixel electrode 4030, the counterelectrode 4031, and the liquid crystal 4008 overlap with each other.

Note that the first substrate 4001 and the second substrate 4006 can beformed by using glass, metal (typically, stainless steel), ceramic orplastic. As plastic, a fiberglass-reinforced plastics (FRP) plate, apolyvinyl fluoride (PVF) film, a polyester film, or an acrylic resinfilm can be used. In addition, a sheet with a structure in which analuminum foil is sandwiched between PVF films or polyester films can beused.

Reference numeral 4035 denotes a spherical spacer which is provided tocontrol a distance (a cell gap) between the pixel electrode 4030 and thecounter electrode 4031. Note that a spacer obtained by selective etchingof an insulating film may be used.

A variety of signals and potential are supplied to the signal linedriver circuit 4003 which is formed separately, the scanning line drivercircuit 4004, or the pixel portion 4002 via leading wirings 4014 and4015 from an FPC 4018.

In this embodiment, a connecting terminal 4016 is formed using the sameconductive film as the pixel electrode 4030 included in the liquidcrystal element 4013. In addition, the leading wirings 4014 and 4015 areformed using the same conductive film as the wiring 4040.

The connecting terminal 4016 is electrically connected to a terminal ofan FPC 4018 through an anisotropic conductive film 4019.

Although not shown, the liquid crystal display device shown in thisembodiment includes an alignment film, a polarizing plate, and further,may include a color filter and a blocking film.

Note that FIGS. 14A and 14B illustrate an example in which the signalline driver circuit 4003 is formed separately and mounted on the firstsubstrate 4001, but this embodiment is not limited to this structure.The scanning line driver circuit may be separately formed and thenmounted, or only part of the signal line driver circuit or part of thescanning line driver circuit may be separately formed and then mounted.

Next, the appearance and cross section of a light-emitting display panel(also referred to as a light-emitting panel) which corresponds to oneembodiment of a semiconductor device will be described with reference toFIGS. 18A and 18B. FIG. 18A is a top view of a panel in which highlyreliable thin film transistors 4509 and 4510 which include semiconductorlayers of In—Ga—Zn—O-based non-single crystal films described inEmbodiment 1, and a light-emitting element 4511, which are formed over afirst substrate 4501, are sealed between the first substrate 4501 and asecond substrate 4506 with a sealing material 4505. FIG. 18B correspondsto a cross-sectional view of FIG. 18A along line H-I.

The sealing material 4505 is provided so as to surround a pixel portion4502, a signal line driver circuits 4503 a and 4503 b, and scan linedriver circuits 4504 a and 4504 b which are provided over the firstsubstrate 4501. In addition, the second substrate 4506 is formed overthe pixel portion 4502, the signal line driver circuits 4503 a and 4503b, and scanning line driver circuits 4504 a and 4504 b. Accordingly, thepixel portion 4502, the signal line driver circuits 4503 a and 4503 b,and the scanning line driver circuits 4504 a and 4504 b are sealed,together with a filler 4507, with the first substrate 4501, the sealingmaterial 4505, and the second substrate 4506. In this manner, it ispreferable that the pixel portion 4502, the signal line driver circuits4503 a and 4503 b, and the scanning line driver circuits 4504 a and 4504b be packaged (sealed) with a protective film (such as an attachmentfilm or an ultraviolet curable resin film) or a cover material with highair-tightness and little degasification so that the pixel portion 4502,the signal line driver circuits 4503 a and 4503 b, and the scanning linedriver circuits 4504 a and 4504 b is not exposed to external air.

The pixel portion 4502, the signal line driver circuits 4503 a and 4503b, and the scanning line driver circuits 4504 a and 4504 b formed overthe first substrate 4501 each include a plurality of thin filmtransistors, and the thin film transistor 4510 included in the pixelportion 4502 and the thin film transistor 4509 included in the signalline driver circuit 4503 a are illustrated as an example in FIG. 18B.

As the thin film transistors 4509 and 4510, highly reliable thin filmtransistors shown in Embodiment 1 including In—Ga—Zn—O-basednon-single-crystal films as semiconductor layers can be used. In thisembodiment, the thin film transistors 4509 and 4510 are n-channel thinfilm transistors.

Moreover, reference numeral 4511 denotes a light-emitting element. Afirst electrode layer 4517 which is a pixel electrode included in thelight-emitting element 4511 is electrically connected to source anddrain electrode layers of the thin film transistor 4510. Note thatalthough the light-emitting element 4511 has a layered structure of thefirst electrode layer 4517, an electric field light-emitting layer 4512,and the second electrode layer 4513, the structure of the light-emittingelement 4511 is not limited to the structure shown in this embodiment.The structure of the light-emitting element 4511 can be changed asappropriate depending on a direction in which light is extracted fromthe light-emitting element 4511, or the like.

The partition wall 4520 is formed using an organic resin film, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition wall 4520 be formed using a photosensitivematerial to have an opening portion on the first electrode layer 4517 sothat a sidewall of the opening portion is formed as a tilted surfacewith continuous curvature.

The electric field light-emitting layer 4512 may be formed using asingle layer or a plurality of layers stacked.

In order to prevent entry of oxygen, hydrogen, carbon dioxide, water, orthe like into the light-emitting element 4511, a protective film may beformed over the second electrode layer 4513 and the partition wall 4520.As the protective film, a silicon nitride film, a silicon nitride oxidefilm, a DLC film, or the like can be formed.

In addition, a variety of signals and potentials are supplied to thesignal line driver circuits 4503 a and 4503 b, the scanning line drivercircuits 4504 a and 4504 b, or the pixel portion 4502 from FPCs 4518 aand 4518 b.

In this embodiment, a connecting terminal electrode 4515 is formed usingthe same conductive film as the first electrode layer 4517 included inthe light-emitting element 4511. A terminal electrode 4516 is formedusing the same conductive film as the source and drain electrode layersincluded in the thin film transistors 4509 and 4510.

The connecting terminal electrode 4515 is electrically connected to aterminal included in the FPC 4518 a through an anisotropic conductivefilm 4519.

As the second substrate located in the direction in which light isextracted from the light-emitting element 4511 needs to have alight-transmitting property. In that case, a light transmitting materialsuch as a glass plate, a plastic plate, a polyester film, or an acrylicfilm is used.

As the filler 4507, an ultraviolet curable resin or a thermosettingresin can be used, in addition to an inert gas such as nitrogen orargon. For example, PVC (polyvinyl chloride), acrylic, polyimide, anepoxy resin, a silicon resin, PVB (polyvinyl butyral), or EVA (ethylenevinyl acetate) can be used. In this embodiment, nitrogen is used for thefiller 4507.

In addition, if needed, optical films, such as a polarizer, a circularpolarizer (including an elliptical polarizer), a retarder plate (aquarter-wave plate, a half-wave plate), a color filter, and the like,may be provided on a projection surface of the light-emitting element,as appropriate. Further, the polarizing plate or the circularypolarizing plate may be provided with an anti-reflection film. Forexample, an anti-glare treatment which can diffuse reflected light inthe depression/projection of the surface, and reduce glare can beperformed.

The signal line driver circuits 4503 a and 4503 b and the scanning linedriver circuits 4504 a and 4504 b may be mounted as a driver circuitformed by using a single-crystal-semiconductor film or polycrystallinesemiconductor film over a substrate separately prepared. In addition,only the signal line driver circuit or part thereof, or the scanningline driver circuit or part thereof may be separately formed to bemounted. This embodiment is not limited to the structure shown in FIGS.18A and 18B.

Through this process, a highly reliable light emitting display device(display panel) as a semiconductor device can be manufactured.

Through this, the light-transmitting transistor or thelight-transmitting capacitor element can be formed in the pixel portionby employing this embodiment to form a display device. Therefore, evenif the transistor or the capacitor element is provided in a pixel,aperture ratio can be made high. Accordingly, a display device with highluminance can be manufactured. Further, since a wiring for connectingthe transistor and an element (e.g., another transistor) or a wiring forconnecting a capacitor element and an element (e.g., another capacitorelement) can be formed by using a material with low resistivity and highconductivity, the distortion of the waveform of a signal and a voltagedrop due to wiring resistance can be suppressed.

This embodiment can be implemented in combination with the structure ofanother embodiment.

Embodiment 2

An element substrate of one embodiment of this invention and a displaydevice or the like including the element substrate can be used for anactive matrix display panel. That is, one embodiment of the inventioncan be carried out in all electronic devices in which they areincorporated into a display portion.

Examples of such electronic devices include cameras such as a videocamera and a digital camera, a head-mounted display (a goggle-typedisplay), a car navigation system, a projector, a car stereo, a personalcomputer, and a portable information terminal (e.g., a mobile computer,a cellular phone, and an e-book reader). Examples of these devices areillustrated in FIGS. 15A to 15C.

FIG. 15A illustrates a television device. The television device can becompleted by incorporating a display panel in a chassis, as illustratedin FIG. 15A. A main screen 2003 is formed using the display panel, andother accessories such as a speaker portion 2009 and an operation switchare provided. In such a manner, a television device can be completed.

As shown in FIG. 15A, a display panel 2002 using a display element isincorporated into a housing 2001, as shown in FIG. 15A. In addition toreception of general TV broadcast with the use of a receiver 2005,communication of information can also be performed in one way (from atransmitter to a receiver) or in two ways (between a transmitter and areceiver or between receivers) by connection to a wired or wirelesscommunication network through a modem 2004. The television device can beoperated by using a switch built in the housing or a remote control unit2006. Also, a display portion 2007 for displaying output information mayalso be provided in the remote control unit.

Further, the television device may include a sub-screen 2008 formedusing a second display panel for displaying channels, sound volume, andthe like, in addition to the main screen 2003. In this structure, themain screen 2003 may be formed with a liquid crystal display panel whichhas an excellent viewing angle, and the cub-screen 2008 may be formedwith a light-emitting display panel by which display is possible withlow power consumption. Alternatively, when reduction in powerconsumption is prioritized, a structure may be employed in which themain screen 2003 is formed using a light-emitting display panel, thesub-screen is formed using a light-emitting display panel, and thesub-screen can be turned on and off.

By employing one embodiment of this invention, a pixel with a highaperture ratio can be formed, whereby a display device with highluminance can be manufactured. Accordingly, low power consumption in atelevision device can be achieved.

FIG. 158 illustrates one mode of a cellular phone 2301. The cellularphone 2301 includes a display portion 2302, operation switches 2303, andthe like. In the display portion 2302, by employing one embodiment ofthis invention, a pixel with a high aperture ratio can be formed,whereby a display device with high luminance can be manufactured.Accordingly, low power consumption in a cell phone can be achieved.

In addition, a portable computer illustrated in FIG. 15C includes a mainbody 2401, a display portion 2402, and the like. By employing oneembodiment of this invention, a pixel with a high aperture ratio can beformed, whereby a display device with high luminance can bemanufactured. Accordingly, low power consumption in a computer can beachieved.

FIGS. 16A to 16C show one example of the structure of a smartphone. Forexample, an element substrate including a thin film transistor and adisplay device including the element substrate, which are shown inEmbodiment 1 are applied to a display portion of the smartphone. FIG.16A is a front view, FIG. 16B is a rear view, and FIG. 16C is adevelopment view. The smartphone has two housings 1111 and 1002. Thesmartphone has both functions of a mobile phone and of a portableinformation terminal, incorporates a computer, and enables various kindsof data processing in addition to telephone conversation, and is alsoreferred to as a smartphone.

The cell phone has two housings the 1111 and 1002. The housing 1111includes a display portion 1101, a speaker 1102, a microphone 1103,operation keys 1104, a pointing device 1105, a front camera lens 1106, ajack 1107 for an external connection terminal, an earphone terminal1008, and the like, while the housing 1002 includes a keyboard 1201, anexternal memory slot 1202, a rear camera 1203, a light 1204, and thelike. In addition, an antenna is incorporated in the housing 1111.

Further, in addition to the above-described structure, the smartphonemay incorporate a non-contact IC chip, a small size memory device, orthe like.

In FIG. 16A, the housing 1111 and the housing 1002 overlap each other.The housing 1111 and the housing 1002 slid to be developed from thestate in FIG. 16A to the state in FIG. 16C. In the display portion 1101,the display device described in the above embodiment can beincorporated, and a display direction can be changed depending on a usemode. Because the front camera lens 1106 is provided in the same planeas the display portion 1101, the smartphone can be used as a videophone.A still image and a moving image can be taken by the rear camera 1203and the light 1204 by using the display portion 1101 as a viewfinder.

The speaker 1102 and the microphone 1103 can be used for videophone,recording, playback, and the like without being limited to verbalcommunication. With the use of operation keys 1104, making and receivingcalls, inputting simple information related to e-mails or the like,scrolling of the screen, moving the cursor and the like are possible.

If much information is needed to be treated, such as documentation, useas a portable information terminal, and the like, the use of thekeyboard 1201 is convenient. The housings 1111 and 1002 overlapping eachother can slide and be developed as illustrated in FIG. 16C, so that thesmartphone can be used as an information terminal. Also, a cursor can beused with smooth operation by using the keyboard 1201 and the pointingdevice 1105. To the jack 1107 for an external connection terminal, an ACadaptor and various types of cables such as a USB cable can beconnected, and charging and data communication with a personal computeror the like are possible. Moreover, a large amount of data can be storedby inserting a storage medium into the external memory slot 1202 and canbe moved.

In the rear surface of the housing 1002 (FIG. 16B), the rear camera lens1203 and the light 1204 are provided, and a still image and a movingimage can be taken by using the display portion 1101 as a tinder.

Further, the smartphone may have an infrared communication function, aUSB port, a function of receiving one segment television broadcast, anon-contact IC chip, an earphone jack, or the like, in addition to theabove-described functions and structures.

By employing the display device described in the above embodiment, asmartphone with improved image quality can be provided.

Note that this embodiment can be combined with any of the otherembodiment as appropriate.

This application is based on Japanese Patent Application serial no.2008-130162 filed with Japan Patent Office on May 16, 2008, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: an oxide semiconductor layer; a gate insulating film; a source electrode of a transistor, the source electrode being electrically connected with the oxide semiconductor layer; a drain electrode of the transistor, the drain electrode being electrically connected with the oxide semiconductor layer; and a gate electrode overlapping with the oxide semiconductor layer with the gate insulating film interposed therebetween, wherein one of the source electrode and the drain electrode comprises a first light-transmitting conductive layer and a first metal layer on and in contact with the first light-transmitting conductive layer, wherein the first light-transmitting conductive layer is in direct contact with the oxide semiconductor layer, wherein the first metal layer does not directly contact with the oxide semiconductor layer, wherein the first metal layer does not overlap with the oxide semiconductor layer, and wherein all side edges of the first metal layer recedes from all side edges of the first light-transmitting conductive layer.
 2. The semiconductor device according to claim 1, further comprising a pixel electrode, wherein the other of the source electrode and the drain electrode comprises a second light-transmitting conductive layer, wherein the second light-transmitting conductive layer comprises indium and zinc, and wherein the pixel electrode is in direct contact with the second light-transmitting conductive layer.
 3. The semiconductor device according to claim 1, wherein the first light-transmitting conductive layer comprises indium and zinc, and wherein the oxide semiconductor layer comprises indium and zinc.
 4. The semiconductor device according to claim 1, wherein the first metal layer comprises copper.
 5. The semiconductor device according to claim 1, wherein the gate electrode comprises a third light-transmitting conductive layer and a second metal layer over the third light-transmitting conductive layer, and wherein the second metal layer does not overlap with the oxide semiconductor layer.
 6. The semiconductor device according to claim 1, further comprising a pixel electrode, wherein the pixel electrode is electrically connected to the other of the source electrode and the drain electrode, and wherein the pixel electrode partly overlaps with the oxide semiconductor layer.
 7. A semiconductor device comprising: a transparent common electrode; a first pixel; and a second pixel, wherein each of the first pixel and the second pixel comprise: an oxide semiconductor layer; a gate insulating film; a pixel electrode; a source electrode of a transistor, the source electrode being electrically connected with the oxide semiconductor layer; a drain electrode of the transistor, the drain electrode being electrically connected with the oxide semiconductor layer; and a gate electrode overlapping with the oxide semiconductor layer with the gate insulating film interposed therebetween, wherein one of the source electrode and the drain electrode comprises a first light-transmitting conductive layer and a first metal layer on and in contact with the first light-transmitting conductive layer, wherein the first light-transmitting conductive layer is in direct contact with the oxide semiconductor layer, wherein the first metal layer does not directly contact with the oxide semiconductor layer, wherein the first metal layer does not overlap with the oxide semiconductor layer, and wherein all side edges of the first metal layer recedes from all side edges of the first light-transmitting conductive layer.
 8. The semiconductor device according to claim 7, wherein the first light-transmitting conductive layer comprises indium and zinc, and wherein the oxide semiconductor layer comprises indium and zinc.
 9. The semiconductor device according to claim 7, wherein the first metal layer comprises copper.
 10. The semiconductor device according to claim 7, wherein the other of the source electrode and the drain electrode comprises a second light-transmitting conductive layer, wherein the second light-transmitting conductive layer comprises indium and zinc, and wherein the pixel electrode is in direct contact with the second light-transmitting conductive layer.
 11. The semiconductor device according to claim 7, wherein the gate electrode comprises a third light-transmitting conductive layer and a second metal layer over the third light-transmitting conductive layer, and wherein the second metal layer does not overlap with the oxide semiconductor layer.
 12. The semiconductor device according to claim 7, wherein the pixel electrode of the first pixel partly overlaps with the gate electrode of the second pixel.
 13. The semiconductor device according to claim 7, wherein the pixel electrode of the first pixel and the transparent common electrode form a first capacitor, and wherein the pixel electrode of the second pixel and the transparent common electrode form a second capacitor.
 14. The semiconductor device according to claim 7, wherein the transparent common electrode does not overlap with a portion where the oxide semiconductor layer overlaps with the gate electrode in the first pixel.
 15. The semiconductor device according to claim 7, wherein the pixel electrode is electrically connected to the one of the source electrode and the drain electrode, and wherein the pixel electrode partly overlaps with the oxide semiconductor layer. 